The cat has gametic traits similar to humans, including teratospermia and many intraovarian oocytes that fail to develop, fertilize or grow in vitro and is therefore an excellent model for human reproduction. The cat also is an excellent model for studying diseases that have transmittal or pathology patterns similar to humans, but these cats often fail to reproduce because of infertility related to inbreeding or the disease itself. Studies of cat oocytes, collected from ovarian material, can provide new insight into the development of rare embryos by providing new knowledge on mechanisms regulating successful in vitro oocyte maturation (IVM), fertilization (IVF) and embryo development. The first aim of this proposal is to examine the relationship of metabolism to oocyte maturation and embryo growth for the purpose of developing a noninvasive index of viability. Secondly, using metabolism as a marker to distinguish oocyte and early embryo quality, we will assess the value of companion embryo culture to enhance developmental potential of embryos produced from lesser quality oocytes. Finally, having elucidated some aspects of embryo interaction in vitro, we will examine the prospect of using asynchronous or heterospecific embryos as companions to improve single embryo development. Our hypotheses are that (1) metabolic patterns are important indices for choosing oocytes with the best chance of fertilization and survival, (2) co-incubating embryos with high quality companions enhances developmental success of embryos originating from 'marginal' oocytes, and (3) that conspecific, synchronous (and older) companions provide greater support than heterospecific and younger companions, but all groups are expected to improve development of solitary embryos. There is applied relevance to (1) providing insight into the combined value of metabolism and companion culture for selecting oocytes for culture and for improving survival of human embryos derived from marginal quality oocytes and (2) rescuing oocytes from cats used as human health models, thereby helping sustain genetically valuable.